ES2606860T3 - Machine tool and method used by said machine - Google Patents

Abstract

A machine tool comprising: a machine base; a first support (200) provided on a first axis of rotation machine (322), with the first axis of rotation mounted on the base in a fixed position with respect to the base; a second support (202) provided on a second axis of rotation machine (324), with the second axis of rotation machine mounted on the base in a fixed position with respect to the base, where the axis of rotation of the second axis of rotation is parallel and is separated laterally from the axis of rotation of the first axis of rotation; an assembly carried by the second support and which is mobile with respect to the second support; and a control arrangement that functions to control the orientation of the first support (200) with respect to the axis of rotation of the first axis of rotation (322), and the orientation of the assembly in relation to the axis of rotation of the second axis of rotation (324 ), so as to govern the position and orientation of the first support and the assembly with respect to each other, characterized in that the machine base comprises a central support (320) located between the machine axes (322, 324), and the axes of machine are mounted on opposite sides of the support.

Description

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DESCRIPTION

Machine tool and method used by said machine.

Field of the Invention

The present invention relates to machine tools and, more specifically, to the reduction of alignment errors in said tools.

Background of the invention

There are numerous applications for machine tools that require the movement of two points in the space so that they are controlled with respect to each other, both in position and at an angle, in a sweeping area or volume. It is convenient to minimize the amount of machine shafts involved to optimize this control. Likewise, it is convenient to maintain a very tight stiffness loop between the two points and, ideally, a constant stiffness value in the loop as the position and angle of the points are adjusted. This improves the level of precision and repetitiveness of the movement.

Often, current machine tools use long linear grinding rails to allow contact between a cutting tool (such as a wheel) and a workpiece in any position along the length of the workpiece. It is possible that the long rails carry the shorter rails to facilitate the movement of a cutting tool to or from the workpiece, in an orthogonal direction to the long rails. These stacked rails (or shafts) provide unwanted elasticity, which reduces the rigidity of the tool to the component. In turn, this leads to reduced component quality, in terms of dimensional accuracy and finish. In addition, it is customary for long-track rails to require, at least, a length equivalent to the workpiece that will be machined. Often, this results in an axis with an insufficient support index where the axis reaches maximum flexibility in the direction of the cutting force. This problem is exacerbated when an orthogonal input shaft is stacked on the long axis.

The use of stacked axes is also problematic if position encoders are used on the axis. The higher the axle stack, the greater the distance between the points of interest and the encoders. This results in "Abbe compensation" errors that reduce the intrinsic precision of machine tools.

Likewise, the use of orthogonal stacked linear axes requires an alignment that is expensive and time-consuming to maintain orthogonality between the axes and minimize the errors of warping, oscillation and balancing of each axis.

These long linear axes also require long telescopic covers that are expensive, provide friction, are prone to failures and, in addition, can influence the precision of linear motion (for example, their straightness, positioning accuracy and repeatability).

The present invention seeks to overcome the problems described above that are associated with the use of long rails and reduce the need for stacked orthogonal axes.

International Publication No. WO2009 / 093064 (in the name of the present applicant) describes a machine tool comprising a machine base, a first support mounted on a first axis of rotation machine on the base, and a second support mounted on a second rotation machine shaft on the base. The second axis of rotation is parallel and is laterally separated from the first axis of rotation, and carries an assembly that is movable with respect to the second support along a first axis of linear machine orthogonal to the second axis of rotation. A control arrangement is provided that functions to control the orientation of the first support on the first axis of rotation, and the orientation of the assembly with respect to the second axis of rotation and its location along the linear axis, so as to govern the position and orientation of the first support and the assembly with respect to each other. This can be achieved without the need for long linear axes or a stacked linear axis, which overcomes the problems associated with the known configurations described above.

Summary of the invention

The present invention relates to a machine tool comprising: a machine base;

a first support provided on a first rotation machine axis, with the first rotation axis mounted on the base in a fixed position with respect to the base;

a second support provided on a second axis of rotation machine, with the second axis of rotation mounted on the base in a fixed position with respect to the base, where the axis of rotation of the second axis of rotation is parallel and is laterally separated of the axis of rotation of the first axis of rotation;

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an assembly carried by the second support and which is mobile with respect to the second support; Y

a control arrangement that functions to control the orientation of the first support with respect to the axis of rotation of the first axis of rotation, and the orientation of the assembly with respect to the axis of rotation of the second axis of rotation, so as to govern the position and orientation of the first support and of the assembly with respect to each other, as described in document US-5,231,587.

According to the invention, the machine base comprises a central support located between the machine axes, and the machine axes are mounted on opposite sides of the support.

Therefore, the forces generated as a result of a rotating machine shaft acting on the other are resisted in tension and compression, rather than in flexion (as is the case with known machine bed configurations). In addition, the stiffness loop and the thermal loop remain substantially independent of the orientations of the machine shafts.

Preferably, the weight of both machine shafts is substantially supported by the central support.

A machine tool described herein comprises: a machine base;

a first support provided on a first rotation machine axis, with the first rotation axis mounted on the base in a fixed position with respect to the base;

a second support provided on a second axis of rotation machine, with the second axis of rotation machine mounted on the base in a fixed position with respect to the base, where the axis of rotation of the second axis of rotation is parallel and this laterally separated from the axis of rotation of the first axis of rotation;

a mounting carried by a support arm on the second support; the support arm being mobile with respect to the second support around a rotary axis; Y

a control arrangement that functions to control the orientation of the first support with respect to the axis of rotation of the first axis of rotation, and the orientation of the assembly with respect to the axis of rotation of the second axis of rotation and its position of rotation around the rotary axis , so that it governs the position and orientation of the first support and the assembly with respect to each other.

This configuration provides benefits associated with the embodiments described in WO2009 / 093064 that are derived from providing two axes of rotation machine provided at a fixed distance from each other. It differs in that the movement of the assembly in relation to the second support is carried out around a rotary axis, the assembly being separated from the rotary axis by means of a support arm, instead of the assembly being movable in relation to the second support along of a linear machine shaft.

As described in WO2009 / 093064, the combination of two rotation machine axes and a linear machine axis facilitates the versatile control of the relative orientations of the first support and a mounting on the second support on a scanning area. The linear component of movement in a plane perpendicular to the first and second axis of rotation is advantageously combined with its rotational movement to, for example, allow grinding cylindrical surfaces by means of a grinding machine comprising this concept.

The author of the invention has understood that the degree of freedom offered by the linear machine axis could actually be facilitated by an additional rotary axis, which obviates the need for a linear axis for this function. With proper control by means of the control arrangement, the rotation of the assembly around its axis can be achieved through the use of an associated drive arrangement to provide the linear motion component of the assembly that is required with respect to the first support. The machine tool can only use these three rotary axes, which facilitates the relative movement between the first support and the assembly, while reducing the susceptibility of alignment errors.

The use of a third rotary axis instead of a linear axis means that the three axes can be rotary axes that can be sealed by using labyrinths that do not provide frictional forces. This is opposed to the protector against linear sliding or cover required by a linear axis. Said protectors or covers tend to be heavy, expensive and provide non-repeatable frictional forces.

Likewise, the use of a third rotary axis is likely to mean that a smaller mass is in motion to create the desired linear component of motion. When a linear axis is used, a relatively large mass that includes the carriage that moves along the axis moves through the second support axis, which alters the polar moment of inertia of the second support assembly to a greater extent . In turn, this may require that the servo loops of the rotating shaft be "adjusted" to avoid instability of the servo over the entire range of polar inertia.

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The term "machine axis" illustrates a physical machine axis herein, as opposed to a reference axis. Each machine axis has two portions that are actuated during use so that they move relative to each other, around or along a reference axis, by associated drive arrangements governed by the control arrangement.

With a grinding wheel mounted on the assembly, the claimed invention facilitates in-depth, conical, angle and interpolation grinding over the full length of a workpiece attached to the first support. It is especially suitable for rectifying thin components of multiple features, such as cams and crankshafts.

The longitudinal axis of a workpiece mounted on the other support can be separated from the axis of rotation of the support, for example with the workpiece near the periphery of the support, so that its total length is easily presentable to a tool on the support. More specifically, the longitudinal axis of the workpiece may be located in an orthogonal orientation to a radial line extending outward from the respective rotation axis.

The third rotary axis can be orthogonal to the axis of rotation of the second axis of rotation machine. Alternatively, it may be in an orientation parallel to the axis of rotation of the second axis of rotation machine.

The supports can be rotated independently around their respective axes of rotation. Alternatively, they may be arranged for rotation so that the rotational movement of one support in one direction corresponds substantially to the equivalent rotation of the other support, but in the opposite direction.

The rotation position of the supports can be selectively immobilized in relation to the machine base. For example, during an in-depth grinding operation, a single axis, namely the rotating shaft of the assembly is "live", which makes the dynamic rigidity of the machine tool during grinding significantly greater than that of a machine Conventional tool that uses only linear rails. Each rotary axis is immobilizable, for example, by clamping the servo, using a brake, or turning off the associated hydrostatic or air bearings to effectively rectify the respective axes.

The supports may be supported on the machine base by means of rotary bearings, preferably by sliding and thrust bearings. Large-size thrust bearings can be mounted directly on the machine base to provide very sharp cushioned shafts with a very good support ratio in all directions, resulting in axisimetric stiffness characteristics. A flat and smooth machine base can be easily constructed to mount the two rotary axis thrust planes on it.

The three rotary axes can use common components, which reduces the total cost of the machine. For example, they can use the same motor, drive, encoder and / or the same bearing components, or the like.

Preferably the bearings of the first and second axis of rotation and of the rotary axis associated with the assembly are in the form of hydrostatic bearings. Linear bearings usually have larger bearing holes than rotary bearings and require the use of thicker (more viscous) oil to maintain flow rates at an acceptable level. For practical purposes, all machine shafts (including a grinding spindle if present) preferably use the same hydrostatic oil. The use of a thicker oil causes greater heating of the oil in a high speed grinding spindle. This can cause spindle overheating problems. Therefore, a less thick oil is preferred for grinding spindles. If all three machine shafts have rotary hydrostatic bearings, then all bearings can have smaller bearing holes and use a lower viscosity oil that is beneficial for the grinding spindle.

The rotation of the supports with respect to the machine base can be carried out by the respective direct drive motors.

Preferably, each support includes a rotation sensor to provide a signal related to the rotation position of the respective support with respect to the machine base. The control arrangement can receive the signals of the rotation sensors and control the rotation positions of the supports. In particular, such a control arrangement can be configured to compensate for the inaccuracy in the movement of these supports during a machining operation. This error correction can be used, for example, to maintain the relative veracity of movement between a cutting tool and a workpiece, rather than simply relying on the straightness of the linear axes of a machine.

In a preferred implementation, one of the supports has a tool assembly, which can be in the form of a grinding spindle or grinding wheel adapted to rotate a grinding wheel mounted on it, for example. The wheel head can be carried by the support arm, and be oriented so that the axis of

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Grinding wheel rotation is parallel to the rotary axis. Alternatively, the axis of rotation of the grinding wheel can be orthogonal to the rotary axis.

Alternatively, or in addition, a support can carry a tool such as a turning tool, one or more calibrators, or sensors, such as a polishing tool inspection sensor, for example. Combinations of tools, calibrators, grinders and the like can be provided on each support and are selected as appropriate by rotating the respective support.

Preferably, the center line of the assembly (and / or center of mass of the tool assembly and the associated tool) has a greater height above the machine base than the center line of the workpiece (and / or its center of mass) . This results in the forces exerted on the workpiece by a tool being directed downwards towards the machine base, which increases the stability of the machine.

Two tool assemblies can be carried by one of the supports, each of which is mobile with respect to the support independently of the other. In this way, two features can be machined on a work piece simultaneously.

Each tool assembly can be carried by a respective support arm on the second support, each support arm being independently movable with respect to the second support around a respective rotary axis. Each support arm can be mounted on a common rod. At least one of the support arms can also be mobile with respect to the support along a linear axis so as to alter the separation of the tool mounts.

The other support may be arranged to support an elongated workpiece with its longitudinal axis in a plane orthogonal to the rotation axes of the rotation machine axes.

A method for machining a workpiece by using a machine tool as defined above may comprise the following steps:

mount a workpiece on one of the supports;

rotate the supports to present a selected portion of the workpiece to a cutting tool carried by the other support; Y

Machining the selected portion of the workpiece with the cutting tool.

In this way, the first and second axis of rotation can be used to bring a cutting tool to the required position along a workpiece. These rotary axes can then be locked and the third rotary axis can be used to feed a cutting tool to the workpiece.

The method may also include the following additional steps:

rotate the supports in opposite directions and move the workpiece and / or the cutting tool with respect to the respective support to couple a second portion of the workpiece with the cutting tool; Y

Machining the second portion of the workpiece with the cutting tool.

With the synchronization of the rotation of the supports and the movement of the workpiece and / or the cutting tool with respect to the respective support, a cutting tool can be traversed along an elongated workpiece, which allows the generation of complex component profiles.

Another method for machining a workpiece by using a machine tool as defined above comprises the following steps:

mount a workpiece that has a longitudinal axis on one of the supports;

rotate the other support so that the axis of rotation of a grinding wheel carried by the other support is not parallel with respect to the longitudinal axis of the workpiece; Y

rectify the workpiece with the grinding wheel with the axis of rotation of the grinding wheel at an angle to the longitudinal axis of the workpiece.

An additional method comprises the following steps:

(a) mount a workpiece on one of the supports;

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(b) mount a tool that has a reference axis on the other support; Y

(c) move the first support with respect to the axis of rotation of the first axis of rotation and the assembly with respect to the axis of rotation of the second axis of rotation and the rotary axis, so that a predetermined profiled or curved surface is defined in the work piece, while maintaining the reference axis of the tool perpendicular to said surface.

A method for calibrating a machine tool as defined above comprises the following steps:

(a) mount a laser light source on one of the supports;

(b) emit a laser beam from the light source that strikes an optical device supported by the other support;

(c) monitor the path of the laser beam with respect to the positions of the supports as measured by the respective rotation sensors;

(d) calculate positioning errors; Y

(e) calibrate the control arrangement so that errors are reduced.

The optical device can be a detector, or a reflector to reflect the incident laser light back towards a detector mounted on the other support, for example. In a preferred implementation, dual laser beams are used and interferometna is used to measure the distance between the laser light source and the optical device.

The use of two primary rotation axes allows the use of software error correction to maintain the position, rectitude and control of angular movement between the two points of interest, instead of having to rely on the straightness of the linear axes of a machine. During the construction of the machine, it is possible to measure the position of the interpolated linear movement between the two points and make software offsets.

The machine tools described herein have a wide variety of potential applications in which the position and angle of two points relative to each other need to be controlled in a sweeping area or volume. In particular, this can be especially beneficial in machining, inspection or positioning of complex components that require position or angle control over a sweeping area or volume. A specific example is diamond turning, where it is often necessary to maintain a cutting tool in a normal orientation with respect to a machining surface.

Brief description of the drawings

Next, the embodiments of the invention and the configurations of machine tools that are useful for understanding the applicability of the invention will be described by way of example, referring to the schematic drawings that accompany it, where:

Figures 1 to 3 are perspective views of the machine tools described in WO2009 / 093064;

Figures 4 to 9 are perspective views of a machine tool to illustrate its operation;

Figures 10 and 11 are side and perspective views, respectively, of a machine tool having a movable grinding wheel around a horizontal rotary axis;

Figure 12 is a simplified perspective view of a machine tool as shown in Figures 10 and 11;

Figure 13 is a perspective view of a machine tool that performs the invention and has a movable assembly around a horizontal rotary axis;

Figure 14 is a perspective view of a machine tool in which a grinding wheel is movable with respect to the second support around a vertical rotary axis; Y

Figures 15 to 18 are perspective views of machine tools that include two support arms that rotate independently around a horizontal rotary axis;

Figure 19 is a perspective view of a known grinding machine to illustrate its variable thermal loop;

Figure 20 is a cross-sectional side view of a machine tool according to an embodiment of the present invention that includes a central support for the two rotation machine axes;

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Figures 21 to 26 are perspective views of a machine tool as shown in Figure 13 in different orientations; Y

Figures 27 to 32 have been made from document WO2009 / 093064 to illustrate the features and capabilities of the described machine tools ALU, which are also applicable to the machine tools described herein.

It should be noted that the Figures are schematic only. The same reference signs are used, in general, to refer to corresponding or similar features in modified and different embodiments.

Detailed description of the drawings

Figures 1 to 3 are schematic perspective representations of the machine tools described in WO2009 / 093064. They include a machine base 10. The first and the second support 100, 102 are mounted directly on the base for rotation around the rotation axes of the respective rotation machine axes, which are perpendicular to the plane of the machine base . Its rotation movement is indicated by arrows A and B, respectively. Points 104 and 106 indicate reference points associated with each support. Each point has a reference axis 108, 110 that passes through it.

An assembly 112 is carried by the second support 102 and is movable along a linear machine axis. The reference point 104 is on the first support, and the reference point 106 is on the assembly 112, carried by the second support 102. The control of the position and orientation of the first support and of the assembly is considered herein with reference to points 104 and 106 and their associated reference axes 108 and 110.

The line representations of strokes 100 ', 102' and 112 'of the first support, the second support and the assembly are included in Figure 1 to show their different orientations after rotation around their respective rotation machine axes. This illustrates the movement to alter the angle between the reference axes 108 and 110.

Figure 2 illustrates the movement of assembly 112 along its linear axis to a second position 112 'shown with a dotted line contour. Arrow C illustrates the direction of movement. This capability facilitates the control of the distance between the two fixed points 104 and 106. The combination of the two rotary axes and a linear axis allows the controlled movement of the points both in position and at an angle in a sweeping area.

Figure 3 shows a machine tool configuration in which the first support 100 is also mobile along the linear machine axis F, which is parallel to its axis of rotation. The position of the support that follows the movement along this axis is shown by the contour of dotted lines 100 '. This additional dimension of movement facilitates the control of the position and orientation of the first support and of the assembly with respect to each other on a scanning volume.

In the machine tools described below, the capabilities of the known machine tool configurations shown in Figures 1 to 3 can be achieved by providing a mount on a support that is movable with respect to the support around a rotary axis, and that It is separated from the rotating shaft by a support arm. A linear component of the movement of the assembly around this rotary axis is used to achieve the linear degree of freedom present in these known arrangements.

The use of the rotary axis to provide a horizontal movement component for assembly is illustrated in Figures 4 to 9.

The first and the second support 200, 202 are mounted directly on the machine base 10 for rotation around the rotation axes of the respective rotation machine axes that are perpendicular to the plane of the machine base. Points 204 and 206 illustrate reference points associated with each support. A reference axis 214 passes through the reference point 204.

A support arm 208 is carried by the second support 202 and is movable relative to the second support around a rotating shaft 210.

Figures 4 to 6 show successive positions of machine tool components as reference points 204 and 206 move over the surface of a notional workpiece represented by a cubic work area 212. As the supports rotate in opposite directions, a constant separation is maintained between the reference points in the direction of the reference axis 214 by rotating the support arm around the axis 210.

The side views of the machine tool orientations shown in Figures 4 to 6 are shown in Figures 7 to 9. A reference line 216 marked on a portion of the support arm 208 which

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extends through the support 202 highlights the changes in the rotation position of the support arm relative to the support.

A grinding machine is shown in Figures 10 and 11. A grinding wheel 220 is provided with its rotation axis 222 in a horizontal orientation and separated from the horizontal rotary axis 210 by a support arm (not visible in these Figures). A workpiece 224 is mounted on the other support 202 (visible in Figure 11). The arrow 226 indicates the movement of the grinding wheel axis along an arc as a result of its movement with respect to the rotary axis 210, the rotation around this axis is identified by the arrow 228.

The horizontal component of the grinding wheel movement around the rotary axis 210 achieves the same horizontal correction movement as the linear machine axis present in the machine tools described in WO2009 / 093064.

Preferably, the motor drive 229 of the third rotary axis is mounted on the second support 202 with its central line parallel to the axis 222 of the wheel head, and in particular with its central line coinciding with the third rotary axis 210. A counterweight 223 is also carried by the third rotary axis to assist with the control of the position of the wheel head with respect to that axis.

Figure 12 shows a CAD model that was used to demonstrate the control math necessary to use rotary motion around a horizontal rotary axis to provide corrective motion.

By achieving this corrective movement by means of a linear axis to provide a straight-line movement between the grinding wheel and the workpiece, the linear correction data remains constant, regardless of the diameter of the part being rectified or the diameter of the wheel. of rectifying With a configuration of the machine as shown in Figure 12, the corrective movement necessary to keep the movement straight (for example) changes with the grinding wheel diameter and the work piece diameter. The rotary axis angles calculated using the CAD model are shown in the following table:

 50 mm part

 400 mm grindstone

   401 mm grindstone

 Angle of the third rotary axis

 Scope Angle of the third rotary axis Scope

 -250 mm

 76,98826862 -250 mm 77.06186038

 0 mm

 71,88021431 5,10805431 0 mm 71,95047563 5,11138475

 250 mm

 76,98826862 250 mm 77.06186038

 51 mm part

 400 mm grindstone

   401 mm grindstone

 Angle of the third rotary axis

 Scope Angle of the third rotary axis Scope

 -250 mm

 77.06186038 -250 mm 77,13546366

 0 mm

 71.95047563 5.11138475 0 mm 72.02074874 5.11471492

 250 mm

 77.06186038 250 mm 77,13546366

Two grinding wheel diameters (400 mm and 410 mm) and two component diameters (50 mm and 51 mm) were used. In the simulation, the grinding wheel was forced so as to keep its grinding edge parallel to the longitudinal surface of the workpiece. It can be seen that the angles of the rotary axes required at the two ends of the components (-250 mm and +250 mm) and at the centers (0 mm) change as the grinding wheel and grinding wheel parameters change. components.

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Thus, with the knowledge of grinding wheel and component diameters, the angular movement around the third rotary axis can be calculated to maintain the necessary movement profile between the cutting tool and the workpiece.

Figure 13 shows another configuration of the machine tool according to an embodiment of the invention. A support arm 230 is capable of pivoting about a third rotary axis 232 in the manner indicated by arrow 234. In the arrangement shown, a grinding wheel head 236 is mounted on the distal end of the support arm so that its axis of rotation is orthogonal to the third rotary axis and to the radial direction with respect to that axis that extends along the support arm. The pivot movement of the arm around the axis 232 results in a movement of the arc grinding wheel head, indicated by arrow 238.

With the support in a generally horizontal orientation, the movement of its distal end around the third rotary axis occurs mainly in the vertical direction.

A flexible joint 240 is used to facilitate rotation of the support arm 230 around the rotary axis 232 in the configuration shown in Figure 13, but it will be appreciated that any type of rotary coupling, such as a rotary bearing, could be employed. The rotary drive force can be provided by a wide range of options, including a motor on the shaft, an off-axis motor (through a belt or gear drive, for example), or a cam drive.

The support arm and the flexible joint are mounted for movement along a linear axis 242 carried by the second support 202. This facilitates the movement of the grinding wheel head to and from a workpiece 244 mounted on the first support 200. This linear movement is also used to correct the horizontal component of the wheel head movement around the third rotary axis 232.

As shown in Figure 13, this movement around the third rotary axis can be used to raise and lower a grinding wheel oriented with its substantially vertical axis of rotation (ie, orthogonal to the third rotary axis and to the support arm). It can then be used to form an edge profile in the workpiece 244 (such as a silicon wafer), for example, or to move the wheel between a workpiece and a grinding wheel that forms the wheel 245 under this.

Another grinding machine is shown in Figure 14. Here, a support arm 250 is capable of rotating around a third rotary axis 252. This axis has a vertical orientation, parallel to the rotation axes of the first and second rotation axis. of the machine The movement of the support arm around this axis in the direction indicated by arrow 254 moves a grinding wheel head 256 around the axis in an arc indicated by arrow 258. This serves to move a grinding wheel 260 mounted on the head grinding wheel horizontally to and from a workpiece 262 mounted on the first support 200.

A tool (in this case the grinding wheel 260) can be moved along an elongated workpiece 262 by rotating the respective supports 202, 200, with a component of the tool's movement around the third rotary axis 252 in a direction perpendicular to the axis of the workpiece that serves to provide corrective motion.

In the configuration shown in Figure 14, it can be seen that the height of the assembly at the end of the support arm 250 remains constant during the operation of the machine. This means that the corrective calculations described above in relation to Figure 12 are not necessary.

In addition, if the arm 250 moves only a few degrees on each side of an orientation parallel to the axis of the workpiece during machine operation, there is only a second order deviation from the desired straight line movement perpendicular to that axis. Therefore, when performing operations that only require small movements perpendicular to one axis of the workpiece, an arrangement in the manner shown in Figure 14 employs a third rotary axis to provide movement close to that of an axis. linear, while using rotating axes only.

Figures 15 to 18 show machine tools that include two tool assemblies. Each tool assembly is carried by a respective support arm 230, 230 '. The tool assemblies are arranged to carry respective grinding wheels at 220, 220 ', with the movement of these around the third rotary axis 210 which provides a respective grinding input. This allows each grinding wheel to rectify a different diameter simultaneously between sf

An independent rotary drive is provided for each support arm together with an associated position encoder. Therefore, each grinding wheel is able to function completely independently of the other. Therefore, two features can be rectified at the same time on a work piece, which can be used, for example, in orbital wrist grinding.

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The support arm 230 is also mounted for linear movement along the rotating shaft 210 to allow variation in the separation in this direction between the two support arms.

Figure 16 shows a view similar to that of Figure 15, except that the support arm 230 has been moved along and parallel to the axis of rotation 210 to be closer to the support arm 230 '.

In the configuration shown in Figures 15 and 16, the two support arms are supported by a sliding bearing rod. In the embodiment shown in Figure 17, the two support arms 230, 230 'are mounted on independent support rods. The support arm 230 is mounted for movement along a linear axis parallel to the rotary axis 210, which facilitates movement in the direction indicated by arrow 270. This facilitates the control of the separation between the two support arms. and the associated tools mounted on them.

An additional configuration of two mounts is shown in Figure 18. Once again, a pair of support arms 230, 230 'are mounted for rotation around a third rotary shaft 210. Instead of a rotary drive on the shaft for each support arm, in the configuration of Figure 18, provides respective linear drive arrangements 280, 280 ', which act in the directions indicated by arrows 282, 282'. Each linear drive is coupled to a respective assembly 284, 284 'through respective pivots 286, 286'. The other end of each linear drive is coupled to the corresponding support arm. The pivot assembly 284 'is movable along a linear axis parallel to the rotary axis 210, which provides movement in a direction indicated by arrow 288. This provides control of the separation between the support arms 230, 230' and the associated tools.

Additional aspects of the present invention will now be described with reference to a known machine tool shown in Figure 19 and an embodiment of the invention shown in Figure 20.

A configuration of the known grinding machine tool that employs long linear axes to rectify an elongated workpiece 224 is shown in Figure 19. A grinding wheel 300 of the grinding wheel is shown in two different locations 300, 300 '. This movement will be necessary to facilitate the coupling of the grinding wheel with the full length of the workpiece.

Each location 300, 300 'has associated "thermal and stiffness loops," schematically indicated by oval 302, 302' in Figure 19. It is well known in this field that the stiffness loop is the shortest path through the mechanical components and the structure of the machine between the cutting tool and the component. The shorter the path, the more sharp the machine will be. The thermal loop is the shortest path through the mechanical components and the structure of the machine between the cutting tool and the component. The shorter the path, the less susceptible to thermal distortions the machine will be.

It can be seen that the locations of the thermal loops 302, 302 'are quite different. If the grinding starts at position 300, it will lead to an increase in the temperature in this region of the machine with respect to the rest, so that as the grinding wheel head moves to position 300 ', it will find a temperature gradient and associated alignment variations.

A typical "throat" movement during a thermal cycle of this machine could be 0.25 mm. The throat is the section of the machine base that connects the grinding wheel assembly with the component assembly. It is the area where the grinding and coolant chips accumulate during the grinding process. Polishing chips and coolant tend to heat the throat material below the grinding zone. The region of the throat that is heated changes, depending on the axial position along the components that are rectified. In the throat region that heats, the material expands, which causes the throat region to open. Over time, the throat is fully heated, which causes it to open. This can cause the grinding wheel position to move away from the component. The motion error will be the maximum where the throat is hotter. As there is no direct measurement of the position between the grinding wheel and the component, there is no feedback system that compensates for errors caused by throat opening.

A machine tool having two parallel rotation machine axes as described herein is shown in Figure 20. An associated thermal / stiffness loop 310 is marked in the drawing. As the axes are rotated to present different parts of a workpiece 224 to a machine tool carried by the support 202, the thermal loop 310 remains substantially unchanged, which avoids the inaccuracies derived from a variable thermal loop. According to the present invention, a central support 320 is provided between the rotation machine shafts 322 and 324.

With a typical horizontal machine bed configuration, the axes are supported from below. In the arrangement of Figure 20, each of the rotation machine axes is mounted on a respective side of the support 320. Each machine axis is coupled to the adjacent side of the support by means of an assembly 326, 328, which extends so horizontal between the respective axis and the support. Thus, the central support or slab carries the weight of each axis of

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machine on either side. Consequently, the forces generated during the operation of the machine tool act through the machine shafts in opposite directions on the central support 320. Thus, the support resists said forces in a state of tension or compression, rather than in flexion, as the case may be with a bed of known machine. This results in a loop of substantially constant (and potentially more sharp) stiffness in the machine tool regardless of the orientations of the support 200, 202. This serves to reduce additional errors during machine operation.

An advantage associated with the configuration of the machine of Figure 13 will now be described with reference to Figures 21 to 26. Figures 21 to 23 show the successive positions of the machine tool when used to rectify one side of a rectangular tile 244 as an example. In Figures 21 to 23, the grinding wheel head 236 moves only along the linear axis 242, and the rotary position of the support 202 around the axis of rotation of the respective axis of rotation machine 324 remains unchanged.

When considering the reference line 340 marked on the grinding wheel 342, it can be seen that the point of contact between the wheel and the tile changes continuously as the wheel moves along the side of the tile. Thus, it is not possible to place coolant nozzles so that they provide optimum cooling and washing during the complete grinding of the tile. An assembly of the articulated coolant nozzle that is capable of tracking the contact point is required.

In contrast, in Figures 24 to 26, the rotary movement by mounting the grinding wheel of the grinding wheel is produced by the rotation axis 324. Consequently, it can be seen that the point of contact between the wheel 342 and Workpiece 244 is constant and is always at the end of reference line 340. This facilitates the maintenance of the optimum conditions of refrigerant application in all parts of the grinding operation, since the optimum location of the nozzle of refrigerant is fixed with respect to support arm 230.

Figures 27 to 32 were taken from WO2009 / 093064. They illustrate the capabilities of the machine tool described in said document, which can be achieved through the use of its configuration of two parallel rotation machine axes, with a linear axis mounted on one of the rotation axes. It will be appreciated that the motion component provided by the linear axis in the configurations illustrated can be provided in accordance with machine tools described herein by a third rotary axis. Therefore, a description of these Figures is included below.

In the machine tool shown in Figure 27, the linear machine shaft is mounted on a rotating shaft. This allows the supports 100, 102 and the assembly 112 to be oriented so that the reference shafts 108, 110 are parallel before the movement of the reference point 106 along the projection of the workpiece. This movement is achieved, then, by the movement of assembly 112 along its linear machine axis only.

The movement with respect to the three axes of the machine can be interpolated to allow access through the reference point 106 to the length of the elongated workpiece 128.

Figure 28 shows the reference point 106 defining a spherical surface 140 equidistant from the reference point 104, while maintaining its reference axis 110 in a "normal tool" orientation perpendicular to that surface.

"Normal tool" maintenance is a common requirement for successful diamond turning of high precision components. It is often essential (to maintain the geometry of the component and the constant cutting conditions) that the same point on the tool remains in contact at all times with the component being machined.

Figure 29 illustrates how the adjustment of the relative rotational orientations of the tool holder 22 and the workpiece holder 20 can be used to create an angle between the rotation axis 50 of a grinding wheel 36 and the axis longitudinal 52 of a workpiece 24, to facilitate the formation of a sharp profile on the workpiece. This principle can also be used to generate other profiles or shapes, such as crown profiles in roller bearings.

Figure 30 illustrates how a preformed grinding wheel 60 can be used by using a machine tool that performs the invention to form predetermined profiles on a workpiece 24.

The machine base can be made of granite, cast iron or polymer concrete, for example and its manufacture can be relatively inexpensive compared to a base for an existing machine tool that uses long linear shafts.

During the construction of a machine tool according to the invention, the precision of the interpolated linear movement between a cutting tool and a workpiece can be measured and any

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necessary compensation. This compensation can be incorporated into the operating instructions of the machine tool controller, for example in software.

The laser calibration can be used with respect to the angle, the linear position and the rectitude correction of movement errors with respect to the rotary and linear axes.

Figures 31 and 32 show how the machine can be calibrated by laser. A light source 70 is mounted on the head 26 that generates two parallel laser beams 72, 74 that are incident on a detector 76 carried by the tool holder 22.

By moving the two axes of rotation and the linear axis, it is possible (by using various laser optics sets) to measure the errors of straightness, position and angle and make the correction to compensate for the errors. Correction procedures will vary depending on the main requirements for any given work piece (for example, parallelism, diameter or axial position of the characteristic that is machined).

The calibration procedure may include the following stages:

I. Use of an angular measurement error optics:

i. Rotate the two axes, linking the secondary axis (for example, the tool support axis) with the primary axis (for example, the work head support axis) over the entire range of motion necessary to machine the component more long. The linear axis will also be linked to the primary axis to maintain a constant position of the laser beam in the measurement optics.

ii. Angular errors will affect:

1. The diameter of the characteristic that is machined;

2. The parallelism of the characteristic that is mechanized;

3. The axial position of the characteristic that is machined;

iii. Any measured angular error can be compensated by modifying the movement of the secondary axis with respect to the primary axis.

iv. This procedure will minimize rotational axis errors (of each encoder) and any additional rotational errors, for example, of inclination errors of the bearing shaft and the oscillation error of the linear axis.

II. Use of linear position measurement optics:

i. Repeat the movement procedure corresponding to (I).

ii. Linear position errors will affect the axial position of the machining feature;

iii. If the axial position of a characteristic has a higher priority than the parallelism of the characteristic that is machined, then the measured position errors can be compensated (by using the secondary rotary axis). This will add slightly to the angular position errors that were minimized during procedure I.

1. The additional angular error could be relatively insignificant. For example, to correct an axial position error of 3 micrometers, an angular correction of 1 arc second is required (approximately). 1 second arc over a 50 mm long feature gives rise to a taper of 0.25 micrometers.

III. Use of straightness measurement optics to determine horizontal straightness errors:

i. Repeat the movement procedure.

ii. Linear straightness errors will affect the diameter of the characteristic that is machined;

iii. The measured horizontal straightness errors can be compensated directly by using the linear axis.

that govern what the

These procedures allow the correction of movement errors without the need to align orthogonal axes, a key benefit of this machine design.

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Preferably, the rotation position of each rotation axis is monitored by the use of respective rotation sensors independent of those used during normal operation of the machine tool. Therefore, these dedicated calibration sensors facilitate calibration independently of normal sensors. The calibration process can then measure and allow the correction of machine movement errors caused by the operating control sensors.

If the axial position of the machined features is particularly difficult, a linear encoder (such as a laser interferometer mounted between the two rotary axes) can be used as a secondary encoder to minimize linear position errors caused by rotary encoder errors.

This can be achieved by applying similar principles to those used in the calibration procedures described above.

The machine tools described herein can use rotary encoders to synchronize movement between two rotary axes. It may be possible to maintain an absolute position error of about 1 second of arc between the two axes. A rotational position error produces a linear error in a given radius of approximately 5 micrometers (linear error) per meter (radius) per second arc (error). For a component of approximately 1500 mm in length, the radius from the center of the rotating shaft to the end of the component may be approximately 900 mm, for example. This results in a linear position error (in the axial direction of the component) of approximately 3 micrometers per second of error arc.

In most cases this will be acceptable. However, for extremely demanding requirements (for example, which require no more than 1 micrometer of linear error) it may be preferable to make a direct measurement in line of linear errors (instead of a linear measurement that is inferred from a rotary encoder ).

An example of a long-range linear laser encoder is an RLE10, as sold by Renishaw (RTM). An encoder of this type could be used to provide linear position feedback as the two rotary axes move relative to each other. Therefore, the resulting axial position errors between the cutting tool and the rotary encoder error component can be measured directly as linear position errors.

The configuration of the linear encoder will be similar to that shown above in Figures 31 and 32 for the machine calibration procedure. However, the laser and the encoder objective require enclosing a cover (not shown in the Figures), far (probably below) from the machining contact position.

The output signals of the sensors used during the calibration procedure are fed to the machine control arrangement or a dedicated calibration processing arrangement. The sensor signals are processed to identify any correction that should be applied to the machine tool control configuration to minimize any detected positioning error.

While the machine tools and configurations described with reference to the drawings are grinding machines, it will be appreciated that a wide range of operations related to machining can be implemented in accordance with the invention. In addition to grinding operations, other applications are turning or polishing, for example, and inspection of machined components.

It will be appreciated that references herein to relative orthogonal or parallel orientations and similar orientations should be interpreted as defining substantially orthogonal or parallel relationships between the components within practical tolerances.

Claims (15)

5 10 fifteen twenty 25 30 35 40 Four. Five 1. A machine tool comprising: a machine base; a first support (200) provided on a first rotation machine axis (322), with the first rotation axis mounted on the base in a fixed position with respect to the base; a second support (202) provided on a second axis of rotation machine (324), with the second axis of rotation machine mounted on the base in a fixed position with respect to the base, where the axis of rotation of the second axis of rotation is parallel and is laterally separated from the axis of rotation of the first axis of rotation; an assembly carried by the second support and which is mobile with respect to the second support; Y a control arrangement that functions to control the orientation of the first support (200) with respect to the axis of rotation of the first axis of rotation (322), and the orientation of the assembly in relation to the axis of rotation of the second axis of rotation (324) , so that it governs the position and orientation of the first support and the assembly with respect to each other, characterized in that the machine base comprises a central support (320) located between the machine shafts (322, 324), and the machine shafts are mounted on opposite sides of the support. 2. A machine tool of claim 1, wherein the weight of both machine shafts (322, 324) is substantially supported by the central support (320). 3. A machine tool of claim 1 or claim 2, wherein the assembly is carried by a support arm (208,230,250) on the second support (202), the support arm being movable with respect to the second support about an axis rotary (210,232,252), and the control arrangement works to control the rotational position of the assembly around the rotary axis. 4. A machine tool of any previous claim, wherein: the assembly is carried by a support arm (208,230,250) on the second support (202), the support arm being movable with respect to the second support around a rotary axis (210,232,252); Y The control arrangement also works to control the position of rotation of the assembly around the rotary axis, so as to govern the position and orientation of the first support (200) and of the assembly with respect to each other. 5. A machine tool of claim 4, wherein the rotary axis (210,232) is orthogonal to the axis of rotation of the second axis of rotation machine (324). 6. A machine tool of claim 4, wherein the rotary axis (252) is parallel to the axis of rotation of the second axis of rotation machine (324). 7. A machine tool of any preceding claim, wherein the supports (200,202) are independently rotatable about their respective rotation machine axes (322,324). 8. A machine tool of any one of claims 1 to 6, wherein the supports (200,202) are arranged for rotation on their respective rotation machine axes (322,324) so that the rotation movement of a support in one direction is corresponds substantially to the rotation of the other support, but in the opposite direction. 9. A machine tool of any preceding claim, wherein the rotation positions of the supports (200,202) are selectively immobilizable with respect to the machine base. 10. A machine tool of any preceding claim, wherein the supports (200,202) are supported on the machine base through sliding and thrust bearings. 11. A machine tool of any preceding claim, wherein the supports (200,202) are capable of rotating with respect to the machine base by respective direct drive motors. 12. A machine tool of any preceding claim, wherein each support (200,202) includes a rotation sensor to provide a signal related to the rotation position of the respective support with respect to the machine base, and the control arrangement functions to receive the signals from the rotation sensors, and to compensate for the inaccuracy in the movement of the supports during a machining operation. 13. A machine tool of any preceding claim, wherein the movement of the support arm (208,230,250) with respect to the second support (202) around the rotary axis (210,232,252) is provided by a rotary bearing. 14. A machine tool of any one of claims 1 to 12, wherein the movement of the support arm (230) with respect to the second support (202) around the rotary axis (232) is provided by a joint flexible (240). 15. A machine tool of claim 14, wherein the flexible joint (240) is movable with respect to the base along the linear axis (242) parallel to the base.